Inserting a small vertical space in a table
use
\rule{0pt}{4ex}
in the first column of that line.
For a general reference on how to improve the spacing in tabular
and array
lines, see the article "Correct spacing for tables and arrays" by Claudio Beccari on p. 10 of TeX and TUG News 1993 (Vol. 2, No. 3).
His method, which involves judiciously inserting "struts", applies to lines in tabular
(as well as tabular*
, supertabular
, xtabular
, longtable
) and array
environments which contain
- superscript material, on a line that's preceded by an
\hline
, - subscript material, on a line that's followed by an
\hline
, and - any other lines with material (including
\hline
s) above or below them that might result in a cramped look of the output.
He suggested defining a "top strut" and a "bottom strut" as follows:
\newcommand\T{\rule{0pt}{2.6ex}} % Top strut
\newcommand\B{\rule[-1.2ex]{0pt}{0pt}} % Bottom strut
Using your MWE as a starting point -- by the way, 9pt
is not a recognized option in the article
document class, so I'm omitting it -- one could put these macros to use as follows:
\documentclass[letterpaper]{article}
\usepackage{helvet}
\renewcommand{\familydefault}{\sfdefault}
\newcommand\T{\rule{0pt}{2.6ex}} % Top strut
\newcommand\B{\rule[-1.2ex]{0pt}{0pt}} % Bottom strut
\begin{document}
\begin{tabular}{ p{8em} r r l }
\hline
& Total & Average & Unit \T\B \\ \hline
Area 1 & 419773 & 9.15 & m\textsuperscript{2} \T \\
Volume 1 & 0 & 0 & m\textsuperscript{3} \B \\ \hline
\end{tabular}
\end{document}
The simplest solution was given by David Carlisle in How to add vertical space struts after hline?
\hline
\noalign{\vskip 2mm}
For those who can use the bigstrut
package, then just inserting \bigstrut[t]
will fix the problem.
\documentclass[letterpaper]{article}
\usepackage{helvet}
\usepackage{bigstrut}
\renewcommand{\familydefault}{\sfdefault}
\begin{document}
\begin{picture}(0,0)
\put(20,-136){\mbox{
\footnotesize
\begin{tabular}{ p{8em} r r l }
\hline
& Total & Average & Unit \\
\hline
Area1 & 419773 & 9.15 & \emph{m$^2$} \bigstrut[t] \\
Area2 & 0 & 0 & \emph{m$^3$} \\
\hline
\end{tabular}
}}
\end{picture}
\end{document}